Cable pathways, conduit and tray

Pathways are the routes and supports that carry communications cable through a building: conduit, cable tray, J-hooks, sleeves through floors and walls, and underground ducts between buildings. Good pathways protect cable performance, keep the building's fire separations intact and leave room to add cable later. Poor ones lead to crushed cable, failed tests, code deficiencies and ceilings full of abandoned wire.

How pathways fit together

Structured cabling follows a hierarchy. Backbone cable runs from the main telecom room, the MDF, to a telecom room on each floor or zone, the IDF, usually through a vertical riser of sleeves or conduits stacked floor to floor. From each IDF, horizontal cable runs to work area outlets, access points, cameras and other devices, carried in tray along corridors and then in J-hooks or conduit to each location. Our guide to telecom rooms: the IDF and MDF explains the rooms themselves.

Types of pathway

ANSI/TIA-569 is the main standard for telecom pathways and spaces, used together with the cabling standards described in structured cabling standards. The Canadian Electrical Code sets rules for communication cables, including their fire ratings and their separation from power conductors, and the building code sets requirements for fire separations and plenums. Check the editions in force in your province.

Conduit

Conduit gives cable the most protection and is the usual choice inside walls, through slabs, in exposed or damp areas and for backbone runs. It is also the least forgiving pathway: once installed, its capacity and route are fixed. Good practice includes:

• Sizing conduit so cable fill stays well below the limit, leaving space for future cables and keeping pulling tension down.
• Limiting the number of bends between pull points, using long-radius bends and adding pull boxes on long or bendy runs.
• Fitting bushings or end fittings so cable is not cut on sharp edges.
• Leaving a pull string in every conduit, and labelling both ends.

Cable tray and J-hooks

Cable tray carries large numbers of cables along main routes and is easy to add to later. It must be supported from the building structure at the spacing the manufacturer specifies, sized for growth and installed with enough clearance above to lay cable in. Tray needs to be bonded so that any fault current has a path to ground, as covered in telecom grounding and bonding.

J-hooks are an economical way to carry smaller bundles from the main tray to rooms. They must be fastened to the structure or to dedicated supports, never to the ceiling grid or its hanger wires, and spaced closely enough that cable does not sag heavily between them. Too many cables in one hook crushes the bottom of the bundle, which can affect the performance of high-speed copper cable.

Separation, interference and fire

Communications cable must be kept apart from power conductors, by distance or by a barrier, as the Canadian Electrical Code requires, and should also be routed away from sources of electrical noise such as motors, transformers, variable frequency drives and some light fixtures. Copper cable carrying high data rates is the most sensitive.

Cable used inside buildings must carry the right fire rating for where it runs. In Canada, cable is commonly marked with flame test ratings such as FT4 for general use and FT6 for plenum spaces, where ceiling voids are used as air return paths. Using the wrong rating is a common inspection deficiency.

Every time cable passes through a fire-rated floor or wall, the opening must be sealed with a listed firestop system suited to that penetration. Sleeves with reusable firestop devices make adding cable later much easier than penetrations that must be re-sealed with putty each time.

What to check on a pathway walkdown

Whether you are accepting new work or taking over an existing building, a walk through the ceilings, risers and telecom rooms with the drawings in hand tells you a lot. Look for:

• Tray and J-hooks fastened to structure, with no cable resting on ceiling tiles, ducts, pipes or the ceiling grid.
• Bundles that are neat, not overfilled, and not pulled tight around sharp corners or crushed by cable ties.
• Cable jackets marked with a fire rating suited to the space, especially in return-air plenums.
• Firestopping in place and undamaged at every sleeve and penetration, including ones disturbed by recent work.
• Separation from power wiring, and no cable strapped to electrical conduit or sprinkler pipe.
• Bonding connections on tray and racks in telecom rooms.
• Labels at both ends of conduits and on tray routes that match the drawings.
• Abandoned cable and empty, unlabelled conduits that should be removed or recorded.

Record what you find with photos and locations. The list becomes the scope for a clean-up project or a set of deficiencies for the installing contractor.

Planning for growth

Pathways cost much less to oversize during construction than to add later, especially in finished ceilings or through slabs. When planning, allow for spare capacity in the riser, spare conduits between buildings, and tray sized beyond today's cable counts. Think about what will be added over the life of the building: more WiFi access points, cameras, building automation devices, and fibre to the floors. Our guide to Cat 6 vs Cat 6A vs fibre covers the cable choices that drive pathway size.

How ehZee can help

We design pathways, telecom rooms and cabling together, including riser and sleeve layouts, tray routes, conduit sizing and firestopping details, as part of our structured cabling design and build service. Electrical work is done by licensed electrical contractors under permit, and drawings for permit are sealed by a licensed professional engineer where required.

Common questions